1. Field of the Invention
All ohmmeters, two-terminal and four-terminal, measure resistance by determining the ratio of voltage to current delivered to a device. In a two-terminal ohmmeter, the voltage and current input to an unknown resistance are through the same circuit, therefore any resistance in the current supply circuit will appear as a part of the unknown resistance because of additional voltage drop. A four-terminal ohmmeter supplies the voltage and current through separate circuits. This allows the voltage to be measured directly at the unknown resistance thus minimizing the effects of resistance in the current supply circuit. A constant current type power source is generally used for the current supply so that the magnitude of current remains constant with any changes of resistance in the circuit. The voltage measuring device has a high input resistance so that changes in resistance of the voltage measuring circuit cause only insignificant changes in the voltage reading.
This invention is a special type electrical connector device that allows the four-terminal concept to be used to measure the unknown resistance while eliminating or minimizing any contact resistance effects of the connector.
2. Background Art
Among the prior art patents which are deemed more or less pertinent to the technology involved in the instant invention is U.S. Pat. No. 3,045,080, which discloses a dual socket, four contact connector device adapted to receive a pair of dual contact pins. However, the thrust of this patent is to facilitate the manufacture of devices where two jacks, switches or combinations may be made in tandem in a single unit. In U.S. Pat. No. 3,108,843, there is also set forth a dual socket, four contact connector for receiving two dual contact pins. However, the expressed purpose of the patent is to provide a jack which is capable of accepting a cable and to provide an insulation from the surrounding panel. U.S. Pat. No. 3,200,355, sets forth plural conductors for each individual pin of a device. However, the conductors do not contact the pins but merely serve as parts of an RF filter within the connector itself. Specific provisions are made to incorporate in an economical fashion the RF filter and capacitor while maintaining functional reliability of the unit. A multiple contact female socket for a single cable is set forth in U.S. Pat. No. 3,278,885. However, it is not disclosed whether the cable is of the single conductor type or whether it contains a conductor for each contact. Hermetic sealing is the main objective of this patent. Lastly, U.S. Pat. No. 3,772,545 relates to a dual contact socket for a two contact pin. The main feature of this reference is the incorporation of a cable plug and side mounted contact surfaces in order to allow installation in hostile environments without extensive buildup. A hermetically sealed system is the prime consideration, even though there is provided surface contacts to establish electrical contact with two internal conductors.
None of the prior art nor any of the above patents disclose a connector for two pin resistive devices to provide increased accuracy of measurement by using a four wire measurement technique, nor do they teach minimizing contact resistance by measuring voltage drop across forward contacts.